Lighting control circuits



"Nov. 11, 1952 e. c. IZENOUR LIGHTING CONTROL CIRCUITS Original Filed Aug. 28, 1947 INVENTOR 60R6 c. IZENOUR BY/ I h H ATTORNEY UNITED STATES "PATENT" OFFICE zss'ls LIGHTING comer. cnwm'rs George C. Isenonn New Haven, Conn. Original No. zsssgiss, dated al-ell 1, 1949, Se-

rial No. 170,999iAug'iist 28, 1947. Application for reissue February 25, 1950, Serial No. 146,380

58 Claims. (01. 315-197) .hhtter enclosed in heavy brackets I: 1 appears in theoriginal patent but forms no part of this specification; matter printed in italics indicates the additions made by reissue.

1 The present invention relates to electrical control circuits for lighting, as in theatres and in television studios.

The currently typical theatre lighting installation has modernization for many years. It includes a large control panel located backstage and off-side, where the operator can view the performance only obliquely. There are large rheostats -that', are connected in series with various lamp banks through plug-boards having individual circuit breakers. The rheostats are necessarily large to dissipate the power reprein the drop in applied voltage when the lamps are operated at les's-than-peak intensity. Obvious wastes of space and power are entailed.

appreciable manual eiiort is required to adjust. each rheostat because oi its large and iirm slid-' in: contacts; and ordinarily one man cannot ad- Just more thali two rheostats simultaneously ,for difierent elfects'j. A few rheostats can be coupled for joint control; but when scoopnected they are"colistrained to operation between like limits and usually be operated simultaneously for fading several lamp banks proportionally between independent limits of intensity.

' The variety and: subtlety of lighting changes are thus narrowly limited.

' rheostat'. being bulky. requires a definite,

large allocation'of space and panel area; so that to be reserved for service when others 39.94 libel! cannot economically be provided, and alteration or expansion of the lighting control equipment is a major undertaking. '1

There have been a few attempts at remote control of stage li ht n in order to get the operator flout front" witlr'the audience for a direct view of the performance. has been accomplished in one instance throughthe use of rheostats operated by motors and electrically controlled clutches. but the initial cost and the space requiremente are considerably increased. In addition an objectionable time lag is introduced between a change of control and its effect. Another remote-controlled lighting control system centersabout saturable reactors. where current determines the saturacan of the coresun the reactors; and these variably the voltage suppiled to the lamps eflicientl'i. without significant power loss exce t for the direct'current in the control circuits. However. a yerysigniflcantpower loss avoidance is aceompaniadby' a very significant time lag lnbetween the change of control and the of eiiect, most pronounced with large loads that large reactors. Furthermore.

inflexible, in that they must be used I with load! or definite uses, within a limited range,

to be eiiective; and they are massive.

With this background my invention will be even a small and inaccessible control room; to

provide a remote-controlled lighting system of such nature that the operator can manipulate many controls independently and can be stationed wherever is best for Judging effects; to devise lighting control circuits of high efflcienc'y in that power not actually consumed in the lamps will be conserved; to provide circuits and methods for eflectively'utilizing grid-controlled gas-type electron-discharge devices in lighting control circuits; to eliminate the mechanical and electrical time-lag inherent in known remote-controlled lighting systems: and to provide a lighting control system built up of interchangeable units, so that replacement and repair of a unit and expansion of the system become relatively simple operations.

A further aim is to provide a control system to enable even an unskilled operator to control many lighting banks in a sequence of scenes with predetermined intensity schedules, from one periormance to others. Equipment of this nature is of particular value in television studios where lighting sequences should be established durin rehearsal. and later unfailingly reproduced promptly and without experimentation during carefully timed broadcasts.

From the foregoing and from the following detailed description of a presently preferred but illustrative application of various features of my invention, it will at once be obvious that almost endless substitution of equivalents, detailed rearrangements and extensions of the novel features may be practicedby those skilled in the art without departing from the spirit of the in-' vention. It should also be understood that certain of its features can advantageously be incorporated in lighting systems of different characteristics than that illustrated, without others of the novel features in the system illustrated.

The drawing is the wiring diagram of the presently preferred embodiment of the invention. showing only two lamps and their control to numerous separate, optionallf correlated lamp cams and control circuits. Incandescent lamps l and II are energized by opposite halves or step-up autotransformer l2 through back-to-bacl: thyratrons I4, l8, l4, l6, respectively. Each of these lighting circuits is. connected between a bright bus It or It and a neutral bus or ground :0 (shown throughout the diagram as a darker line). The autotransfcrmer divides the line voltage to provide a neutral with a roughly balanced load on each side. Autotranstormer l2 boosts the resulting divisions of the line voltage to compensate for the internal voltage drop in the thyratrons and the autotransformer itself so that lamps of standard voltage ratings can be used. Thus.- trons are chosen for moderate loads, and this term is intendedi tc represent any appropriate grid-controlled gas -type electron-discharge devices generally. Each pair of thyratrons provides independent control for its series lamp, a1- though it will appear that coordinating controls are also available. Each lamp Ill and II is representative of a single lamp or a lighting bank that optionally includes many lamps, up to the current limit of the thyratrons.

Under proper conditions of grid excitation each thyratron can be made conductive during substantially an entire half of an altemating-current cycle. The pairs of thyratrons, because of their back-to-back connection, can supply lamp current throughout the alternating current cycle when maximum intensity is desired. By properly adjusting the grid excitation of the thyratrons the firing of each can be retarded, for lower light intensities. A change of this adjustment is instantly followed by a change in light intensity, for no heavy iron-cored inductor is included in the lamp circuit.

The thyratron grids are here supplied with alternating current, and their control efiect is attained by controlling the phase of the grid alternating current and represent a resistance the magnitude 0! which depends on the grid drive. A pair of resistors 28 and 20 are also connected across buses l8 and 20, the junction of the resistors furnishing a voltage reference point.

The primary winding ll of thyratron grid transformer 22 is connected between the Junction of these resistors/ and the Junction 26 or the condenser 28 and vacuum tubes 22, 24. (A trimmer mister is sometimes desirable between condenser 2i and junction 36; so that the latter does not necessarily exist as a tube-condenser junction.) Separate secondaries 1B and 38a are con-,

nected between the respective grids and cathodes of thyratrons i4 and it, through the usual rid current limiting resistors.

is negative, its grid voltage is of no concern; for

. the voltage on the grid of the associated thyradrive in relation to the plate alternating current I supply. Where the grid voltage is in phase with the plate supply or somewhat leading, the thyratron plates will be conductiveduring substantially complete half-cycles because the instantaneous grid voltage will be positive at the start of the positive half-cycles of the plate. By applying lagging voltage between the thyratron grids and cathodes, the firing of the thyratrons can be de-.

layed during each half-cycle, since thegrid voltage remains negative during theelapsing first part of each positive half-cycle of the plate. By controlling the phase of the grid voltage, the time-division during which current is supplied to the lamps can be varied to change the eiIective current, although the instantaneous current during the conductive intervals may not vary significantly. In this waythe energy supplied to the lamps from fixed-voltage lines is efllciently varied, without the large power waste characteristic of the series resistors so commonly used in lighting control.

thyratron-lamp circuit. Sections 22 and 21 are enclosed in a common envelope for convenience only; they may readily be replaced by separate vacuum tubes, and will therefore be treated as separate tubes. Tubes 22 and 24 together pass tron will control the time of firing of that thyratron during the positive half-cycle of its plate. In the subsequent halt-cycle the plate' polarities are reversed, and at the same time the grid control voltage is reversed. to establish the desired control relation in the previously idle.

vided by the back-to-back vacuum-tube phase control network.

In firing, each thyratron suddenly imposes a load on the line. Many lighting loads may be assembled in any given scene, with certain of them operating at diflerent intensities. Because of this, there may be dlsturbances'in line voltage caused by early-firing thyratrons that have some unplanned effect on the control circuits of the later-t'o-be-flred thyratrons, tending to produce flickering. To minimize the effect of line-voltage transients caused by other lighting circuits and by miscellaneous loads, and partly for added flexibility of the control equipment, I have found that excellent stability of control can be realized through supplying full-wave rectified alternating current to the grids of vacuum tubes 22 and 24.

The reason for improved flexibility will become clear as the disclosure continues.

The grids of vacuum tubes 22 and 24 are connected to the negative output terminals of selenium dry-disc full-wave rectifiers ID and 42,

energized by secondaries II and IQ of transformer 48, the center-taps of the secondaries being connected to the respective cathodes of vacuum tubes 22 and 2|. By controlling the amplitude of voltage supplied to grid transformer 48, the plate resistance of tubes 22 and 2| can be varied widely,

trolled magnitude of alternating-current voltage supplied is converted to variable controlled revidual sistance, and then to phase-controlled voltage for the thyratron light-intensity re lators. A Thyratrons It and I6. transformers I! and II, vacuum tubes 22 and I4, condenser I. and

' resistors 28 and 3| together comprise a control and 'ccntrci units are connected. Unit 40 is interchangeable for unit 9' and for other control units. They occupy a minimum of space, are readily removed, repaired when necessary, and installed and these features facilitate alteration and expansion of any given installation to meet changing lighting requirements. Only one phase of power for input transformers 4|, 4|, etc., is required whether the controlled lighting circuit is connected to bright bus II or to bright bus II. This flexibility, mentioned previously. is attributable to rectiilers II and II which not only smooth out the transients impressed on the vacuum-tube grids, but also eliminate phase reversal diiilculties.

Units 4!, ll and so, on include the thyratrons which pass lighting currents that are heavy, and for this reason the units are located near the lighting center, assembled in a rack in any available space. The operator is stationed at any convenient point where the lighting effects can be viewed directly, remote from the bank of control units. Between the operator's position and the control bank there is a cable including a pair of low-current power lines and a lar e number of control lines to transformers 4|, 4|, etc.

Two adjustable networks are available to the operator. Both networks are energized by stepdown autotransformer ll. connected between one input terminal of autotransformer if and neutral. Both networks are useful in a single installation for different purposes. The networks are similar in that they both include a master potentiometer and at least one group of potentiometers individual to each lighting bank over which separate control is or may be desired.

- The simpler control network of the two is termed the Individual Proportional Master. A variable autotransformer I2, used as the master potentiometer. is connected at its input terminals to autotransformer BI: and has a series of individual potentiometers It, It, et'c., connected at their input terminals to the adjustable output portion ll of the potentiometer. An individual potentiometer is provided for each lighting bank II, it, etc. The power required of .each potentiometer II is very low. only enough to energize one small transformer 4! and its rectifier and negative-grid load. Consequently the individual potentiometers can be miniature sliding-tap resistors so inexpensive and readily available. The output portion of each individual potentiometer is-connected through a double-pole double-throw transfer switch ll. through the connecting cable, to its respective input trans- ,former in unit. il etc. when the, Individual Proportional Master is opera through its master potentiometer l2. all of the light banks are varied between darkness and the several brightness limits as fixed by the several indipotentiometers. This variation is uniform and proportional; no light bank reaches its maximum intensity .before the others. In the operator's booth the individual potentiometer-s are arranged for easy access, so that an individual light bank can be readily adjusted as circumstance may demand without aflecting the others.

The other control network for units ll is termed the Fader and is energized by the same autotransformer II that supplies the first control network It includes sliding-tap autotransformer is as itsemaster potentiometer, having adjustable complemental portions 82 and N. The latter portion is on the neutral side of the fixed-voltage supply line. The primary winding of unity-ratio transformer I! is connected across output portion '2 oi-master 6|, and one of its secondary terminals is grounded. A series of miniature sliding-tap resistors Ila'. 10b, 10c. etc.. termed preset potentiometers or simply presets, is connected across the secondary of transformer 08. A second series of presets 12a, 12b. 12c, etc.

is connected across the grounded output porswitch deck ll. having contacts rgc. Nb, 'IIc,

etc., is arranged to connect any selected slide contact of presets ll through transfer switch I! to one input terminal of unit Ii. Similarly, another selector-switch deck I. having'contacts 16a, lib, 18c. etc., is arranged to connect any selected slide contact of presets 12 through transfer switch to the. other input terminal of unit 49. The output portions of presets II and 12 are thus connected in series to energize unit ll, and their junction is grounded. This symmetry of the presets about neutral or ground is a factor promoting safety and facilitating construction, and is the controlling reason for including the unity-ratio transformer.

v The phasing of transformer It is such that its output is series-aiding with respect to the output of portion ll of master potentiometer CI. The voltage across preset I0 and 12 in series thus remains constant at the terminal voltage of master ll regardless of the position of its slide contact, the internal voltage drops in parts II and BI being disregarded as negligible. By moving the slide of master it from one extreme to the other, the terminal voltage of the master can be shifted from the selected preset II to the selected preset l2 and reversely, One preset or the other remains in the circuit, to the extent of its output portion, without delivering voltage; but the input impedance of unit ll-is by design so high in relation to the total series resistance of any selected pair of presets (a factor of twenty-five is desirable) that the inclusion of part of the idle preset in the output circuit of the energized preset is of little consequence. The arrangement is of considerable advantage in fading from lighting control by one preset to control by the other preset of any selected pair II and If. The brightness varies smoothly from the limit determined by the setting of one preset to that fixed by the other preset, with noobjectionable dip into darkness. Of course. if

ferent levels of intensity, this could be accom-'- plished by setting a preset of one group at sero and shifting from one preset of the other group to the zero preset and then to a second preset of the first group. I I

, During the times when one preset is eflective. the idle one can be adjusted if desired. although this would not be usual. However, switches II and I! are of such construction that at least one pair of their contacts is closed in all posi* tions of adjustment; and with this provision the selector switch of the idle preset can be manipulated for a new selection. sequentially as from position a to b or otherwise. without aifecting the lighting control circuit to transformer ll. When a new selection has been made, and the scene requiring the eflective presets is over,

other group can be switched after fading toav preset in the previously idle group.

Additional groups of presets It and 12' (in cluding presets 10a, lllb' and flak 12b. are connected to the same master 6' and transformer 68 as for presets Ill and 12,,for controlling unit 49' of lamp bank It. Corresponding selector-switch decks l4 and 16 are also provided. Switch decks H. II, etc. (one for each lamp bank to be controlled) are mechanically ganged to constitute one selector switch. and switch decks II. II. etc. are similarly ganged to constitute a second selector switch. It is thereby made possible to fade from one complete array of preset lighting conditions to another, smoothly and proportionally, simply by manipulation of master potentiometer 60' from one extreme to the other. Selection of a new preset lighting array is achieved simply by operation of either selector switch", l4. or selector switch ll, ll? while the other remains in the circuits of the effective presets. For special effects or in case of emergency it is also possible to switch over to the Individual Proportional Master network by throwing any desired one or group of transfer switches 58. With the aid of a pro-- set array in each selector switch set for darkness. it becomes possible to fade into dark from any given preset selection, transfer to the other network by throwing all transfer switches =58, and then operating its master 52 from zero to maxi mum. Convenient variation of intensity of any s sizes of lamp banks up the thyratrons, and the units are of such naturethat expansion to meet new lighting requirements is comparatively an'easytask. None of the ponderous components and unwieldy controls of previous lighting control systems are required. The

system is highly emcient. For the most part it utilizes such small parts as are commonly found in radio receivers; and the thyratronsconsume very little power in comparison to the lamps they control. As an indication of scale, Master 60 of, one ampere rating can simultaneously supply about 200 presets and their control units.

Theforegoing represents a preferred lighting control system illustratin several separately and collectively useful features of my invention, as pointed out in the appended claims.

What is claimed is:

1. A phase controller for the grid of a electron-discharge device in series with a lamp energized by an alternating-current source, comprising a voltage divider connected to the source.- a grid-controlled vacuum tube and a reactive impedance connected in series and to the terminals of said voltage divider, a coupling circuit between a point intermediate said vacuum tube and said impedance and a tap of said voltage divider for controlling the gas-type device, and a widely adiustable source 'of controlled voltage for the grid of said vacuum tube. I

2. The method of controlling illumination intensity of an alternating-current lamp in a circuit having a series thyratron, comprising the steps of supplying a voltage variable in magnitude [inrelation to] as uv definite junction of the desired 'intensity, converting the [controlled] magnitudemriable voltage to a corresponding two-directionally conductive resistance,- [and] deriving.

or several light banks,- individually by means of ing requirements of a sequence of dramatic incl-f dents can be preset, and the operator can fade from one to the next smoothly and expeditiously. irrespective of the desired number of lamp banks of diifering peak intensities. This control can be duplicated from one performance to the next. The flexibility of controljachieved with the presets can be extended by amaze to the individual controls as described. restricting the transfer to only the desired banks. The nature of the control units and their control networks is such that the changes of intensity follow instantly with the operation of the controls, without the electrical and mechanical lags characteristic of known remote-controlled lighting systems. The control networks that may be located far from the heavycurrent lighting circuits aresimple, compactand inexpensive. The heavy-current control units 49 are interchangeable, they may be used for all Using the control system described, the light-T therefrom an alternating-current thzrratron-timing voltage the phase of which is critically related to that of the lamp circuit [for timing theiiring of the thyratron appropriately for], and utilizing;- said thyratron-timin voltage to varythe c011.-v ductive intervals of the thuratron junction of the desired intensity.

3. A controller for the grid of a gas-type electron-discharge device in series with a lampenergized by an alternating-current source, comprising a voltage divider connected to said source an. electrically variable resistance and .an impedance connected in series to the terminals of said voltage divider, [and] said resistance having control electrade means, an output circuit for controlling said grid and having input connections between step in said voltage divider and the point intermediate said impedance and said variable resistance, and variable voltage-applying means connected to said control electrode means.

4. A phase-controller for the grid of a. gas-type electron-discharge device in series with a lamp energized by an alternating-current source; comprising a voltage divider connected to said source. a back-to-back pair of grid-controlled wacuum.

tubes, a reactive impedance in a series circuit with said pair of tubes, said series circ'uit being connected to the terminals of said voltage divider. an output transformer having its primary wind.-

ing connected to a point between said tubes and vsaid impedance and to a tap of said voltage die.

vider, and an adjustable alternating-current supply i'orv the grids of said vacuum tubes and coupled a to the alternating-current source that energizes 1 said voltagedivider. a

5. A phase-controller according. to claim 4, in.- cluding a dry-disc full wave rectifier between said.

to the maximum rating'of as-typ I .as a definite"- a iu tab c .sl ati sr e tsunp v and, eachalternating-current voltage source, and separate a coupling circuits between said source and each of said .grids, said circuits including means polarized to drive both grids alike in relation to their cathodes when the related plates are driven positive.

.7. In combination, a variable-intensity lamp, 9. phase-responsive control circuit for said lamp, a series circuit including a reactive impedance and. .a. back-to-back pair iol grid-controlled vacuum tubes, circuit means for providing a voltage reference point, said series circuit being connected toan alternating-current source at its terminals and at an intermediate point to a. .control terminal of said phase-responsive circuit, said reference point being connected to another control terminalo/ said phase-responsive circuit, and an adjustable control for the grids, oi said vacuum tubes.

8. In combination, a variable-intensity lamp. a phase-responsive control circuit for said lamp, a series circuit including a reactive impedance ,and a back-to-back pair of grid-controlled -vacuum tubes, circuit means for providingv a voltage reference point, said series circuit being connected at its terminals to an alternating current source and at a point intermediate said impedance and said vacuum tubes to a control terminal said phase-responsive control circuit, said reference point being connected to another control terminal of said phase-responsive circuit, a rectified alternating-current supply for 'controlling said vacuum tubes, and a potentiometer for controlling the input to said supply.

I 9. In combination, a variable-intensity lamp, a phase-responsive control circuit for said lamp, and a variable phase-shift circuit for said control circuit, said phase-shift circuit including a vacuum tube the internal resistance of which is variable as a function of the applied control voltage, and an individual potentiometer and "a master potentiometer arranged in cascade to control said vacuum tube, the illumination intensity being variable by said master potentiometer up to the limit fixed by said individual potenti ometer.

110; In combination, an array of variable-intensity lamps, a phase-responsive control circuit foreach lamp, a phase-shifting network for each control circuit including a vacuum tube the internal resistance or which is variable as a function of the applied control voltage, a control circuit for each of said phase-shitting networks including a preset potentiometer, and a master potentiometer 'i'or gradually intensifying the illumination of said array of lamps to limits severally fixed by said preset potentiometers.

- 11. In combination, a variable-intensity lamp, a phase-responsive control circuit for said lamp, a phase-shifting networkior said control net-. work including a, vacuum tube the internal resistance'oi' which is variable as a iunction oi the applied control voltage, and an adjustable source of control voltage for said vacuum tube including said tap, whereby adjustment of said master potentiometer from one extreme tov the opposite adjusts the lamp from a maximum fixed by-one of said preset potentiometers to. a maximum fixed by the other of said preset potentiometers.

12. In combination, a variable-intensity lamp, a phase-responsive control'circuit for said lamp, a phase-slutting network for said control circuit including a vacuum tubethe internal resistance 0! which varies as a function oi the "applied control voltage, and a variable voltage supply unit including a pair 01 preset potentiometers having their output sections connected in series and coupled in control relation to said vacuum tube,

a master potentiometer having an adjustable tap, and an isolating unit, the portions of, said master potentiometer on opposite sides of said tap being connected, respectively, to the input end or said isolating unit and to the terminals of one or said 7 put end spanned by the other of said preset limits fixed by the selected preset potenticm i the other of said switches by operating said potentiometers, said isolating unit being so hased that adjustment 01' said master potentiometer from one extreme to the opposite extreme will cause variation of the intensity of said lamp irom a maximum limit as fixed by one of said preset potentiometers gradually and without reversal to the maximum limit as fixed by the other or said potentiometers.

14. In combination, an array of variable-intensity lamps, a. control unit i'or'each oi 'said lamps, a plurality of pairs oi preset potentiometers,

said pairs having output portions connected in series and to a respective one of said units, and a master potentiometer having 'complemental sections, one section-being coupled to the terminals of one preset potentiometer oigeach pair and the other section 01' said master potentiometer being coupled to the terminals of the others of said pairs of preset potentiometers,- whereby adjustment of said master potentiometer from one extreme to the opposite extreme will cause said lamps to fade from their bright limits as fixed severally by one preset potentiometer of the pairs proportionally to the several limits fixed by the other preset potentiometers in the respective pairs.

15. In combination, an array oi -variablelntensity lamps, a control unit for each lamp, a plurality oi preset potentiometer-s for each unit, a pair of selector switches each having. multiple ganged sections corresponding to the number of control units and arranged to connect said preset potentiometers to said units in pairs, and a master potentiometer having complemental portions, the preset potentiometers of one 01' said selector switches being coupled to one 0! said portions and the preset potentiometer-s or; the other of said selector switches being coupled to the other of said portions, whereby the illumination intensities of the lamps can be changed from the several limits fixed by the selected preset potentiometers of one oi said switches to the several cters' aasrs master potentiometer from one extreme to the other.

18. An arrangement for applying alternating current from asource to a'load comprising a master potentiometer having complemental sections, a transformer having its primary connected across one of said sections, a preset potentiometer connected across, the other oi said sections, another preset potentiometer. connected across the secondary of said transtormer, the output portions of the preset potentiometers being connected 'in series across the load and so phased by the transformer as to be series-aiding when said master potentiometer is in any intermediate position of adjustment, the Junction of said preset potentiometers'being joined to a fixed terminal of said master potentiometer.

17. The combination of the arrangement 01 claim 16 with a load spanning said series portions of said preset potentiometers, the impedance oi the load being at least ten times that oi either preset potentiometer.

, 18. A phase control network comprising a voltage divider, a series circuit including a pair or vacuum tubes connected back-to-back so that one tube is conductive during each half of an alternating-currentv cycle of applied voltage, said pair of tubes being connected in series with a reactive impedance across said voltage divider,

i an output circuit connected to a tap in said voltage divider and toga point in said series circuit between said vacuum tubes and said impedance, and a variable control for said vacuum tubes.

19. A phase shifter comprising a voltage divider, a series circuit including a vacuum tube ,and a reactive impedance'co'nnected across said voltage divider, an output circuit connected to a tap in said voltage divider. and to a point in said series circuit between said .vacuum tube and said impedance, and a variable control circuit for said vacuum tube including a full-wave rectifier and a denser and tubes, and the grid and cathode of the r gas-type electron-discharge device [and a point in said series circuit between said condenser and said tubes].

21. Alighting control circuit comprising a pair 0! gas-type tubes connected together in a manner to provide a current path during successive halves of an alternating-current cycle and having control electrodes, a-series circuit including a condenser and a back-to-back pair' of vacuum tubes having control grids, circuit means providing a voltage reference point, a transformer having two secondary windings connected respectively to said control electrodes and having a primary winding connected to said series circuit and said reference point, and a variable control circuit connected to said grids.

22. A lighting control circuit comprising a pair of gas-type tubes connected together in a manner to provide a current path during successiv halves of an alternating-current cycle and having conimpedance and a parallel pair of reversely polarized variable resistance devices each being substantially non-conducting in one direction and having a control element for varying the resistance, "circuit means providing a voltage reference point, a coupling circuit [between] for the control j'electrodes and cathodes" of said gas-type tubes, said circuit running from said reference point and a point in said series circuit between said reactive impedance and said parallel devices, and an adiustable control circuit connected to said elements.

23; A variable-intensity lighting system comprising a lamp, a back-'to-back pair or thyratrons in a series circuit with said lamp, said series circuit having terminals for energization by an alterhating-current source, and a network connected in control relation to said thyra'trons includihg a pair of vacuum tubes'connected to said terminals for coordinated energization with said thyratrons.

each of said vacuum tubes including a grid, a cathode, and a plate, and having variable gridcontrol means, the plate of one of said tubes being Joined directly to the cathode of the other of said tubes in back-to-back relation. H

24.. A control circuit for a variable intensity lighting system including a grid-controlled gastype tube connected in a circuit to alternatingcurrent supply terminals and a phasing circuit connected to the grid of said tube including a condenser and a pair of unidirectionally conductive devices connected to said condenser providing charging and dischargin Paths, at least one or said devices having a control element adapted to impart a variable-resistance characteristic, and a control circuit connected to said control element. v

25. [A] In a phase control network [comprising], a condenser and a pair of vacuum tubes connected in series to alternating-current terminals, each of said tubes having a plate, a cathode, and a control grid, the plate-cathode spaces of said tubes being connected in parallel circuits and the plate of one or said tubes being connected to the cathode of the other, and an adjustable [voltage-] supply for applying voltage adjustable in magnitude to said control grids.

26. A controlled lighting circuit having power supply terminals for alternating-current 81121? gization, comprising a lamp load and a back-to back pair of thyratrons Joined in series and connected to said terminals, a voltage-responsive phasing circuit coupled through a two-secondary transformer in control relation to said thyratrons. said phasing circuit including a series-connected condenser and back-to-back pair of vacuum tubes, each tube having a control grid, a variable voltage supply including a transformer having a pair of secondary windings connected through rectifiers to said control grids in such polarity as to drive said grids negative, a potentiometer in said variable voltage supply having an adjustable output section connected to said transformer and having fixed terminals, an a variable voltage divider having an adjustable output section connected to said fixed terminals, said variable voltage dlvider and said phasing circuit having stable.

connection to said power supply terminals.

27. A controlled lighting array having a variable voltage divider and a plurality of lamp loads. phasing circuits, and variable voltage supplies in accordance with claim 26, the adiustable'output section of said variable voltage divider being cantype .nected to the'terminals oi! the potentiometers in 1 said variable voltage supplies.

.28. A controlled lighting array in accordance with claim 2'7 wherein said power supply terminals separated from said lamp loads by a centertapped. autotransiormer with certain oi said lamp-loads connected on one side of the center- ;tap. and the .remainder of the lamp loads connected on the opposite side of the center-tap, said variable voltage divider being connected on one side or the center-tap, and wherein said rectiilers are, or the full-wave rectifier type.

29. An alternating-current circuit including a pair vacuum tubes each having a grid, a cathode, and a plate, the plate-cathode spaces of said tubes being connected in parallel circuits with the cathode of one tube connected to the .plate oi th other, means to apply alternatingcurrent voltage to said parallel circuits, and

means to apply unidirectional voltages of like adjustable value to the-grid-cathode spaces of said tubes. '30. An alternating-current circuit including --a polarized] arranged to maintain said grids negative with respect to the related cathode during the conductive half-cycle of the respective tubes,

and a common means to impress alternating-,

current voltage on said grid-cathode circuits.

31. A variable-resistance alternating-current 'circuit comprisinga back-to-back pair of reversely polarized unidirectionally conductive and "variably resistive devices each having a control electrode, means to impress alternating-current voltage on said back-to-back devices, and means to impress like voltages on said control electrodes during the respective halt-cycles o! impressed voltage when said devices are conductive.

'32. s phase controller for the grid of a gaselectron-discharge device in series with a lamp energized by an alternating-current source, comprising a voltage divider connected to the source, a back-,to-back pair of reversely polarized unidirectionally conductive and variably resistive "device?! each of which has a control terminal, a

reactive impedance, said back-to-back devices and reactive impedance being connected in series across the terminals of the voltage divider, a

coupling circuit between a point intermediate said back-to-back devices and said impedance and d tap of said voltage divider for controlling the gas-type device, and a widely adjustable :source' of voltage for the control terminals of said backto-back devices.

33. In a method of variably energizing an alternating-current lamp in a circuit, that improvement including the steps of supplying a control voltage variable in magnitude in definite relationship to a desired intensity of illumination of the lamp, converting the control voltage to a corresponding, two-directionally conductive resistance, with the aid of said resistance producing an alternating-current voltage the phase of which is critically related to that of the lamp circult. utilizing the critically phased voltage to vary the conductive intervals of a thyratron as a definite direct function of the desired intensity, and using the discharge current of the thyratron to energize the lamp.

' .34. A controller for the grid of a gas-tyn eleci tron-discharge device in series with a lamp energized' by an alternating-current source, comprising a voltage divider connected to said source.

an'electrically variable resistance and an impedance connected in series across the terminals of said'voltage divider, said resistance having high impedance control electrode means. an output circuit for controlling said grid and having input connections between a tap in said voltage divider and thepoint intermediate said impedance and said variable resistance, and means connected to .said control electrode means to apply thereto a controlled voltage variable in amplitude.

35. A phase-controller tor the grid 0/ a gastype electron-discharge device in series with a lamp energized by an alternating-current source, comprising a voltage divider connected to said source, a back-to-back pair of grid-contrblled vacuum tubes. a'reactive impedance in a series circuit with said pair of tubes, said series circuit being connected to the terminals of said-voltage divider, an output transformer having its primary winding connected to a point between said tubes and said impedance and to a top of said voltage divider, and means for supplying alternatingcurrent adjustable in amplitude to the grids of said-vacuum tubes, said last named means-ineluding a circuit in phase with the voltage across the voltage divider.

36. For use in controlling the intensity of an alternating-current lamp, a phase-responsive control unit for said lamp, a phase-shifting network for said control unit, said network including "a' vacuum tube the internal resistance of which is variable as a junction of the applied voltage, and an adiustable source of'control voltage connected to apply grid voltage to said'vacuum tube,'said source including a master potentiometer having an adjustable tap and a pair of preset potentiometers having their output sections coupled to said :vacuum tube and their input terminals coupled'to the sections of said master potentiometer on opposite sides of 'said tap, whereby adjustment .0! said master potentiometer from-one extreme to the opposite adjusts the lamp from a maximum deed by one otsaid preset potentiometers to a maximum fixed by the other of said preset potentiometers.

37. For use in controlling the intensity of an alternating-current lamp, a phase-responsive unit for said lamp, (1: phase-shifting network for said control unit, said network including a vacuum tube the internal resistance of which is variable as a lunctiono! the applied voltage, and an adjustable source of control voltage connected to apply grid voltage to said vacuum'tube, said source including aplurality of presettable voltage control devices, and means gradually. to transfer energization from one. to another of said devices.

38. For use in controlling the intensity of an alternating-current lamp, a -phase-responsive control circuit for said lamp, a phase-shifting unit for said control circuit, said unit having a high input impedance, a plurality oj .,prese'ttable low impedance voltage control devices connected in series and to apply voltage to said unit, a first variable voltage means to energize one of said devices, a second variable .voltag'e means to energize another of said devices, said first and second variable voltage means including coordinating means to increase the voltage output of either of said variable voltage means coordinately with decrease of the voltage output of the other 0/ said means.

39. In a phase-shifting'network, a condenser connected in a series circuit with a patrol gridcontro led vacuum tubes, said tubes being arranged in parallel circuits and oppositely polarized [or full-cycle conductivity, and a control cir-- cuit for applying voltage of adjustable magnitude to said vacuum tubes.

- 40. A phase-shifting network comprising a voltage divider, a condenser connected in a series circuit with a pair of grid-controlled vacuum tubes across the terminals of the voltage divider, said tubes being arranged in parallel circuits and oppositely polarized for full-cycle conductivity, said tubes having grids, and means to supply an adjustable control voltage to said grids.

41. A thyratron control circuit for adjustably energizing an alternating-current lamp, said circuit including in combination a thyratron having grid-and-cathode input terminals and a phaseshift circuit having alternating-current energizing connections and connected in control relationship to said thyratron input terminals, said phase-shift circuit including a condenser and a grid-controlled vacuum tube connected in series, said vacuum tube being conductive during alternate halfrcycles of the supplied alternating-current, adjustable control means for said vacuum tube and a unidirectionally conductive device in parallel with said vacuum tube and polarized to be conductive during the half-cycle in which the vacuum tube is non-conductive.

'42. A phase-control network comprising four legs connected in a loop, said network adapted to have a voltage input applied across a pair of junction points connecting diflerent pairs of legs and to have an output voltage taken from the remaining pair of junctions, one of said legs including a condenser, another of said legs including a pair of grid-control vacuum tubes arranged in parallel circuits and oppositely polarized for full-cycle conductivity and a control circuit for said vacuum tubes.

' 43. For use in a system wherein an alternatingcurrent lamp is energized by the discharge of a thyratron, wherein the thyratron firing is controlled by a phase-shifting network and wherein said network includes an alternating-current device whose impedance is variable as a function of voltage applied to control terminals thereof, means for supplying an adjustable control voltage to said device, said means comprising a pair of presettable control elements connected in series and coupled to the control terminals, and means to selectively energize either one of said elements to adjust the lamp intensity between limits successively determined by said presettable elements.

44. For use in a system wherein an alternatingcurrent lamp is energized by the discharge of a thwatron, wherein the thyratron firing is controlled by a phase-shifting network and wherein said network includes an alternating-current device whose impedance is variable as a function of voltage applied to control terminals thereof, said device having a high input impedance, means for supplying an adjustable control voltage to said device, said means comprising a pair of Pres'ettable low impedance control elements connected in series and coupled to the control terminals,

'. and means to selectively energize either one of said'elements to adjust the lamp intensity between limits successively' determined by said presettable elements.

- 45. For use in a system wherein an alternatingcurrent lamp is energized by the discharge of a thyratron, wherein the thyratron firing is conries and transformer-coupled to the control ter-rminals, and means to selectively energize either one of said elements to adiustthe lamp intensity between limits successively determined by said. presettable elements. j;

46. For use in a system wherein an alternatingcurrent lamp is energized by the discharge of a thyratr'on, wherein the thyratron firing is 'controlled by a phase-shifting network and wherein said network includes a grid-controlled vacuum tube, means for supplying an adjustable voltage to the grid of said vacuum tube. said means com-,. prising a pair of presettable control elements connected in series and coupled to the control terminals to apply a negative voltage to the grid ofthe tube, and means to selectively energize either one of said elements to adjust the lamp intensity between limits successively determined by said presettable elements. 1

47. For use in a system wherein an alternatingcurrent lamp is energized by the discharge of a thyratron, wherein the thyratron nring is controlled by a Phase-shifting network and wherein said network includes an alternating-current device whose impedance is variable as a junction of voltage applied to control terminals thereof, means for supplying an adjustable control voltage to said device, said means comprising a plurality of presettable control elements, means to connect a selected pair of said elements in series to said control terminals, and means to selectively energize any one of the elements selected pair. r

48. For use in controlling the intensities o) a plurality of lamps, a plurality of control units each controlling a difl'erent lamp, a set of presettable potentiometers for each control unit,

switch means for selectively connecting a pair of said presettable potentiometers from each set to its associated control unit, and common means 49. For use in controlling the intensities of a plurality of lamps, a plurality of control units each controlling a diflerent lamp, a plurality of presettable potentiometers, switch means for selectively connecting a digerent pair of said presettable potentiometers to each control unit, and common means for gradually shifting energization from one potentiometer of each of said pairs to the other potentiometer of each of said pairs."

50. In an alternating current circuit, the method of controlling illumination intensity of a lamp so as to attain any desired lamp intensity over a wide range, including the steps of supplying a control voltage variable in magnitude in deft-J nite relationship to a desired intensity of illumination of the lamp, and independent of the lamp current, converting the control voltage to a corresponding two-directionally conductive re-' sistance, with the aid of said resistance produc ing an alternating-current voltage the phase of which is critically related to that of the lamp circuit, utilizing the critically phased voltageto vary the conductive intervals of a thyratron in a definite direct relationship to the desired lamp.

ssprs intensity, and using the discharge current of the thyratron to energize the lamp.

51. A circuit for controlling the illumination intensity of a lamp from an alternating-current source, said circuit including a gas type electron discharge device directly feeding the lamp by series connection, a phase-shifting network for said device, said network including a phase-shift controlling vacuum tube the internal resistance of which is-variable as a function of the grid voltage, and an adjustable source of control voltage connected to supply grid voltage to said vacuum tube, said last-named source including a plurality of presettable voltage control devices and means gradually to transfer energization by the alternating current source from one to another of said devices.

52. A circuit for controlling the illumination intensity of a lamp from an alternating-current source, said circuit including a gas type electron discharge device directly feeding the lamp by series connection, a phase-shifting network for said device, said network including a high inputimpedance variable component for controlling the shift in phase of said network, the regulation of said component being controlled by voltage magnitude, and an adjustable source of control voltage for said component, said source including a plurality of presettable low impedance voltage control devices connected in series and connected to said high input-impedance component, and means gradually to transfer energization by the alternating-current source from one to another of said devices.

53. A circuit for controlling illumination intensity of a lamp from an alternating-current source, said circuit including a ilas type electron discharge device directly feeding a lamp by series connection, a phase-shifting network controlling the firing of said device, said network including an -lternating-current device whose impedance is variable as a function of voltage applied to control terminals thereof, means for supplying an adjustable control voltage to said last-named device, said means comprising a pair of presettable control elements connected in series and coupled to the control terminals, and means to selectively energize either one of said elements -to adjust the lamp intensitybetween limits successively determined by said presettable elements.

54. A circuit for controlling illumination intensity of a lamp from an alternating-current source, said circuit including a gas time electron discharge device directly feeding a lamp by series connection, a phase-shifting network controlling the firing of said device, said network including an alternating-current device whose impedance is variable as a function of voltage applied to control terminals thereof, said last-named device having a high input impedance, means for supplying an adjustable control voltage to said last-named device, said means comprising a pair of presettable low impedance control elements connected in series and coupled to the control terminals, and means to selectively energize either one of said elements to adjust the lamp intensity between limits successively determined by said presettable elements.

55. A phase controller for the grid of a gastype electron-discharge device in series with a lamp energized by an alternating-current source, comprising a voltage divider connected to the source in parallel with the series-connected gastype device and lamp, a grid-controlled vacuum tube and a capacitor connected in series and to the terminals of said voltage divider, a coupling circuit between a point intermediate said vacuum tube and said capacitor and a tap of said voltage divider for controlling the gas-type device, means providing a direct-current discharge path for the capacitor, said means including a portion of the voltage divider and a direct-current-conductive impedance between said portion of the voltage divider and the point intermediate the vacuum tube and the capacitor, and a widely adjustable source of controlled voltage for the grid of said vacuum tube.

56. For use in controlling the intensities of a plurality of lamps in series with gas-type electron-discharge devices, a plurality of control units each controlling a different device, a set of presettable potentiometers for each control unit, switch means for selectively connecting a pair of said presettable potentiometers from each set to its associated control unit, and common means for gradually shifting energization from one potentiometer of each of said pairs to the other potentiometer of said pairs.

57. For use in controllin the intensities of a plurality of lamps, a plurality of control units each controlling a different lamp, a plurality of presettable potentiometers, switch means for selectively connecting a different pair of said presettable potentiometers to each control unit, and a high impedance circuit coupling the selected presettable potentiometers to the associated lamp.

58. For use in controlling the intensities of a plurality of lamps in series with gas-type electron-discharge devices, a plurality of control units each controlling a different device, a plurality of presettable potentiometers, switch means for selectively connecting a different pair of said presettable potentiometers to each control unit, common means for gradually shifting energization from one potentiometer of each of said pairs to the other potentiometer of each of said pairs, and a high impedance circuit coupling the selected presettable potentiometers to the associated electron-discharge device.

GEORGE. C. IZENOUR.

REFERENCES CITED The following references are of record in the file of this patent or the original patent:

UNITED STATES PATENTS Number Name Date 1,914,193 Bedford June 13, 1933 2,001,836 Craig May 21, 1935 2,001,837 Craig May 21, 1935 2,001,838 Craig May 21, 1935 2,005,893 Gulliksen June 25, 1935 2,054,496 Craig Sept. 12, 1936 2,076,108 Young Apr. 6, 1937 2,231,955 Shrader Feb. 18, 1941 2,242,105 Brettell May 13, 1941 2,376,392 Shepherd May 22, 1945 2,411,030 Ryder Nov. 12, 1946 2,458,644 Ringer Jan. 11, 1949 2,474,886 Bovey July 5, 1949 FOREIGN PATENTS Number Country Date 747,996 France ....4 Apr. 10, 1933 OTHER REFERENCES December 1943. 

